Question 1

Which of the following statements best describes a zwitterion at physiological pH?

Accepted Answer

A molecule with both positive and negative charges, but an overall net charge of zero.

Question 2

Which amino acid does NOT have a chiral alpha carbon?

Accepted Answer

Glycine

Question 3

At which wavelength do proteins typically show maximum UV absorbance due to aromatic amino acids?

Accepted Answer

$280\ \mathrm{nm}$

Question 4

Calculate the isoelectric point ($pI$) for glycine given $pK_1 = 2.34$ and $pK_2 = 9.60$.

Accepted Answer

$pI = \frac{2.34 + 9.60}{2} = 5.97$

Question 5

Which amino acid would have a net charge of $+2$ at low pH?

Accepted Answer

Arginine

Question 6

Why is peptide bond formation in cells coupled to ATP hydrolysis?

Accepted Answer

Because peptide bond formation is thermodynamically unfavorable and requires energy input.

Question 7

Which of the following best describes the primary structure of a protein?

Accepted Answer

The unique, defined sequence of amino acids in a polypeptide chain.

Question 8

Which enzyme would you use to cleave a peptide specifically at the carboxyl side of lysine residues?

Accepted Answer

Trypsin

Question 9

A peptide bond forms between which two groups of adjacent amino acids?

Accepted Answer

The carboxyl group of one amino acid and the amino group of the next.

Question 10

Which of the following amino acids absorbs UV light most strongly at 280 nm?

Accepted Answer

Tryptophan

Question 11

If the pH of a solution is increased, what happens to the overall charge of a peptide?

Accepted Answer

It becomes more negative.

Question 12

Which of the following is true about the hydrolysis of peptide bonds?

Accepted Answer

It is thermodynamically favorable but kinetically slow without a catalyst.

Question 13

Which property distinguishes L-amino acids from D-amino acids?

Accepted Answer

Their configuration around the alpha carbon.

Question 14

Which of the following best explains why aspartic acid has a net charge of $-2$ at high pH?

Accepted Answer

Both the alpha-carboxyl and side chain carboxyl groups are deprotonated.

Question 15

Which of the following is a correct formula for calculating the isoelectric point ($pI$) of an amino acid with two ionizable groups?

Accepted Answer

$pI = \frac{pK_1 + pK_2}{2}$

Question 16

Which of the following best describes a polyampholyte?

Accepted Answer

A molecule with multiple positive and negative charges.

Question 17

Which of the following statements about peptide bond stability is correct?

Accepted Answer

Peptide bonds are stable under physiological conditions but can be hydrolyzed by proteases.

Question 18

Which of the following is a real-life application of peptide bond cleavage?

Accepted Answer

Proteases in the digestive system breaking down dietary proteins.

Introduction to Proteins: The Primary Level of Protein Structure (Chapter 5 Study Notes)

Study Guide - Practice Questions